Berkshire almost doubled its stock purchases in the third quarter, including a big investment in Combs favorite MasterCard. MasterCard was a major part of Combs' portfolio at his hedge fund, Castle Point Capital Management, which he shuttered to join Berkshire.

"I wonder if he turned Todd Combs loose," David Rolfe, chief investment officer at Wedgewood Partners, which invests in Berkshire, told Bloomberg News. "I hope Buffett went to the movies one day and Combs got on the phone and went crazy with buy orders."

All told, Berkshire invested $23.9 billion in the third quarter, its biggest three-month buy in 15 years. Almost $7 billion of that was in stocks, increasing Berkshire's equity holdings by 62% to $17.4 billion.